1. Field of the Invention
The present invention relates to a voice coil motor, and more particularly, to a voice coil motor with a lateral attraction force.
2. Description of the Prior Art
In order to perform a more accurate position control for a set of lenses or an access arm of a hard disk drive, a voice coil motor (VCM) is adopted to move the set of lenses or the access arm of the hard disk drive. The structure of a VCM is primarily a coil placed within a magnetic circuit including a permanent magnet.
In an optical system employing a VCM, there is an interaction propelling force between the coil and the permanent magnet according to Fleming's left-hand rule that moves a carrier physically connected to the permanent magnet when a current flows through the coil; at the same time, a set of lenses which is attached to the carrier is moved correspondingly, so as to achieve optical zoom and focus functionalities. Based on applying a specific current value through the coil, an accurate control for optical zooming and focusing can be achieved.
In an optical system employing a VCM, the attractive force in a lateral direction between a magnetic device and a plurality of guide posts of the VCM causes friction force between a lens carrier and a plurality of guide posts. The added friction force is sufficient to maintain the lens carrier and other devices thereon at a specific position without applying the current to a coil. For example, Taiwanese Patent Application No. 1400861, entitled “VOICE COIL MOTOR APPARATUS WITH STABLE MOVING”, as shown in FIG. 6A˜6B, the voice coil motor comprises the lens carrier 80 (mainly constructed by a set of magnetic sensing elements), the guide posts 801 and 802 and electromagnetic drive mechanism (mainly constructed by the coil) on the base 200. After the lens carrier 80 is equipped with the base 200, the guide posts 801 and 802 fixed on the base 200 contacts against the opening structure 701 and 702 of the lens carrier 80.
Based on the attraction force of the set of magnetic sensing elements, the guide posts 801 and 802 fixed on the base 200 contacts against the opening structure 701 and 702 of the lens carrier 80 and the lens carrier 80 is rotated along the R direction. Based on rotation of the lens carrier 80, there is at least one contacting line C6 between opening structure 702 and the guide posts 802, and there are at least two contacting line C4 and C5 between opening structure 701 and the guide posts 801.
A flatness requirement of the opening structure 701 and 702 of the lens carrier 80 is higher for maintaining the contacting line C4, C5 and C6 in a straight line and stable moving of the lens carrier 80. However, A flatness requirement of the opening structure 701 and 702 of the lens carrier 80 is too hard to be successfully produced in quantity.